The Northeast is facing the threat of flash flooding this week from unusually strong storms that could dump up to a month’s worth of rain in just a few days in parts of the region.
This flooding system is caused by a pocket of energy that is driving severe thunderstorms across parts of the Great Lakes and Ohio Valley on Monday. Power outages and strong wind gusts that can knock down trees are the main threat in these areas, but isolated tornadoes are also possible. An “extremely dangerous” tornado struck northeastern Wisconsin Monday afternoon.
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On Tuesday, this energy will pivot toward the Northeast, where it will either intensify or decelerate dramatically. It is expected to last at least Thursday in parts of the region.
The strength of the storm as it passes through central New York on Wednesday will be comparable to what is expected to occur in October, November or December, rather than late July. Storms are typically weaker in the summer than in the winter because the jet stream has less energy to strengthen the storm.
At the same time, the system taps into a pipeline of Atlantic and Gulf moisture that has risen to well-above-average levels even in the middle of a notoriously humid midsummer.
These extremes will collide, producing multiple rounds of heavy rain and thunderstorms across the Northeast.
Areas from the New York tri-state area to Philadelphia are at greatest risk of flooding Tuesday and Tuesday night, but the localized threat covers most of the rest of the Northeast.
Heavy rain will fall from eastern New York to Pennsylvania in the morning, with more rain possible in the afternoon and evening. The most severe storms can produce more than an inch of rainfall per hour.
Floods are most of concern in urban areas and areas with poor drainage, but it is unclear whether this week’s flood impacts will rise to a more severe level, as they have occurred multiple times this month across the country, including in New York City on July 18.
Further south, the threat of severe thunderstorms is expected from around Washington, D.C., to North Carolina on Tuesday. When a storm intensifies, the biggest concern is wind damage.
The most widespread flash flooding threat will move slightly north on Wednesday to southern New England, including Boston and Hartford, but New York City will also remain at risk.
Heavy rain is likely to continue in the region as the day begins. One or more narrow bands of heavy rain will move northeast into the afternoon, potentially causing flash flooding. New storms are also possible behind this region.
The National Weather Service in Boston said at least sporadic flash flooding is possible, especially in urban areas and areas with poor drainage. Travel delays are possible at airports and roads throughout the region.
Parts of the Northeast may continue to see locally heavy rain on Thursday, but it’s too early to determine specific flooding concerns.
Many flood-prone areas in the Northeast are expected to receive 1 to 4 inches of rain by Thursday.
Higher amounts could occur in places where the heaviest rain falls or where bands of rain slow or stop falling over several hours. These locations are also more likely to experience more severe flooding impacts.
The storm is expected to weaken and move out of the Northeast by Friday, but scattered showers and storms are still possible over the region.
